Process of aromatizing a naphtha with an alumina-chromia-platinum catalyst



PROCESS OF AROMATIZING A NAPHTHA WITH AN ALUMlblA-CHROMIA-PLATI- NUM CATALYST Harold A. Strecker, Bedford, and Harrison M. Stine, TLyndhurst, Ohio, assignors ,to The Standard Oil (Jmpany, Cleveland, Ohio, a corporation of Ohio No Drawing. Application 0ctober8, 1952 Serial N 313,786

2 Claims. (Cl. 208-136) This invention relates to the catalytic conversion of hydrocarbons, and more particularly to catalytic reforming.

1n gatalytie reforming, relatiuely light petroleum fractign s, such as naphthas and gasolines containing .an a

preciable amount of paraifin sand naphthenes, are treated rates Patent at an elevated temperature in theipresence of acatalystto that catalysts and reaction conditions that promote re forming also promote cracking more or less. It is believed that the cracked products polymerize under the reaction conditions, and that-the end product of the polymerization is coke. This cokeformation is not primarily jap'roduct 2,870,084 Pa e ted n- 20 195,

e u of hydro n an the Pr c s doe n tb wnis non-regenerative even at hydrogen partial pressures high enough for near complete repression of the reforming reactions. I a

Inasmuch as the use of hydrogen cannot completely prevent colge formation and only at :best repress it, it.

is desirable to pe ate a lowe h dro en art a arr s. a r ore low rt t l Pressu es if othe variables can be selected which will give a low coke deposition at the low pressures. Not only is the construction of reaction equipment facilitated by :theuse of low pres- I sures, but the passage from the reforming to the regen-. crating cycle is facilitated if the reforming operation' is carried out at a low pressure. Regeneration at high pressures is not practical, so that if the reaction pressure is 7 high, complicated equipment, such as locks, must be provided for changing the pressure between the reaction and the regeneration. If the pressure is sufficiently low,

the difference between the reaction pressure and atmospheric regeneration pressure can be taken care of in the" fluid type equipment with a leg of catalyst as is well I understood in the art.

In'accordance with our invention, we have discovered I that hydrocarbons may be reformed utilizing-a co-pre' cipitated alumina-chromia catalyst containing a small amount of an oxide of platinum or palladium (or both) under reforming conditions using a relatively low hydroof the reforming. Rather it is 'bel-ievedthat the .eolie.

results from the cracking-polymerization reactionswhich take place concurrently with the reforming. As a result, a deposit of coke is laid down on the catalyst and the rate at which this .coke .is deposited .dependsupOn the conditions of conversion and upon the catalyst. 11;! gene cral, conditions which give a high conversion level result in' increased coke deposit. In most of the usual cases,

especially thoseemploying oxide type catalysts, the coke gradually destroys the activity-=of the catalyst for promoting the desired conversion. loss in catalyst activity necessitates the regeneration of the catalyst generally by burning off the coke. It is highly desirable, therefore, .to provide processes using conditions and a catalyst which will minimize (the deposition of coke during the reforming conversion.

This desirability of a mlnimum coke-producing reforming conversion is economically attractive from the standpoint of savings in capital expenditure for regeneration, equipment, or the loss of on stream t1me if the regen I eration ,is done in the same equipment, as well as in sayings of feedstock. Particularly is this lso when it is desired to operate the process at high conversion levels where coke production ordinarily represents a greater problem.

.It has been .proposed heretofore to carry out the reforming conversion in the presence of addedhydrogen,

and it has been found that the'excess hydrogen :tends to decrease the amount of coke deposited, probably due to the repression of the polymerization reactions. The presence of hydrogen, however, inhibits thereforrning reaction to some extent and requires increased temperatures :to produce the same quality of product that is produced in :the absenceof hydrogen at lower temperatures: However, coke .formation is not eliminated by gen partial; pressure and low operating pressure, togive a ch hi he le e v o con r on With an corre po g i t ase in k po i io Qr. n the alter point of view, a minimization of coke depositionaththe conversion levels, as compared with catalysts previously known when operated under the same conversion eondi- In addition, the relatively low hydrogen partial pressuresuseable with this catalyst provide an optimum 1 yield-octane relation and minimize butane production.

tions.

'Prior Patent No. 2,236,514, assigned to'our assignee,

describes a gel-type catalyst of alumina and chromia in r the proportions of 70-82 mol percent alumina and 18-30 mol percent chromia formed by co-precipitating precursors of-these two-ingredients. A preferred'embodirnent described in the patent consists in co-precipitating a catalyst to provide '80 mol percent alumina and '20 I mol percent chromia by treating nit-ratesof the two metals with ammonia. Catalysts with proportionsof the two oxides within the ranges stated may be made by other i co-precipitating methods such as the reaction of sodium aluminate with a soluble chromium salt such as chromium nitrate or chromium-acetate, with adjustment-ofthe pH up to-about 10, if necessary.

Merely as illustrative, such a catalyst may be prepared by mixing solutions of chromium acetate and sodium aluminate in proportions to provide a co-precipita'ted catalyst having 76-mol percent offalumina and 24- niol percent chromia accompanied by the addition of sulfuric acid to maintain a pH of about 8.5. The catalyst 'is washed free of sulfate, dried and has 3% volatiles at This catalyst was used in a reforming operation'employing a naphtha having a Kattwinkel number of about 10.5 (AnS. T. M. Standard Method-D875-46Twhich is a measure-of olefins and aromatics), an initial boiling point of 222 F., 50% over at ZSZT'F. and an end point i of 397 F. The reforming conditions were as follows:

Temperatureof conversion 980 F. Total pressure (gauge) 25 1138.138! square Hydrogen to naphtha mol ratio 4.9. Hydrogen partial pressure (absolute) Feed rate 1.32 v.'v. h. On stream time- 30 minutes.

inch.

33 lbs. per square inch.

The reformed product as obtained was analyzed for Kattwinkel number as a measure of the reforming con version. The catalyst after being flushed with nitrogen and cooled was analyzedfor coke by a conventional carbon determination method utilizing Combustion in a quartz tube. The following results are typical of the average of a large number of conversions with slight extrapolation to the higher conversion:

Kattwinkel number: Coke, wt. percent Kattwinkel numbersin the range of 55 to 65 correspond approximately to octane numbers of 80 to 90 by the F-1 method.

Considering that coke percentages in excess of 3 to 386% are excessive for a commercial operation, it will be seen that while this catalyst is one of the best available, the extent of the conversion with the permissible coke conversion, has its limits.

It has also been proposed heretofore in Patent Nos. 2,250,415 and 2,410,044 to add a small amount of antimony oxide to such a catalyst as a third component. When a catalyst comprising 73.7 mol percent alumina, 24.6,mol percent chromia, and 1.7 mol percent antimony oxide was used in conversions on the same naphtha and under the same conditions described heretofore, the following results are typical of numerous experiments with slight extrapolation to the upper conversion level:

Kattwinkel number:

Coke, wt. percent so a '60 2.2 '70 3.3

carbon fractions such as naphthas and virgin gasolines,

under reforming conditions utilizing a low pressure, and in the presence of a co-precipitated chromia-alumina catalyst impregnated with a relatively small amount of an oxide of platinum or palladium or both. While all three components may be co-precipitated, we find the catalyst entirely suitable when the chromia and alumina are co-precipitated and the third element incorporated by impregnation. as that described heretofore and may be made by the same methods, i. e., co-precipitation of alumina and chromia within the ranges described heretofore. Catalysts used in the process of the invention may be impregnated with a solution of a salt of platinum or palladium which can be converted to the oxide upon heating. The concentration ofthe solution and the length of the impregnating time are such as to incorporate the desired amount of the third oxide which may be from 0.001 to about 1.0 mol percent. In general, the catalyst is treated with the solution in a concentration of 0.0001 to 0.10 mol per liter. The catalyst may be treated with the impregnating solution for from a'few minutes to several days, dependon the concentration of the solution and the amount to be absorbed, the excess solution drained away, and the catalyst dried. The catalyst is then heated at a high The catalyst base maybe the same temperature such as 850to 1250 F. for a period of four to. twenty-four hours in an atmosphere of a gas such as dry nitrogen and cooled in the similar atmosphere. During this heating the impregnating element was converted to the oxide.

The catalyst may be in any of the usual physical forms, more particularly, in particles of any size'or shape. It the catalyst is finely divided, the reformingoperation may be carried out with the catalyst in a fluidized condition using the so-called fluid reforming technique. The

catalyst may also be in larger particles, such as beads,

' which are more commonly used in the fixed and moving bed techniques.

The reforming operation is carried out under any of the usual reforming conditions provided the pressure is relatively low, which is an advantage of our process. In general, the temperature will be between 800 to 1200 F., preferably 900 to 1000 F. The total pressure will be from atmospheric to about pounds, preferably about 25 pounds, per square inch gauge and the conversion conducted in the presence of added hydrogen to provide a hydrogen partial pressure of about 10 to about 85, preferably 10 to 50, pounds per square inch absolute. The rate of feed may be maintained at from about0.3 to

' 10 volumes of hydrocarbon'feed per volume of catalyst per hour.

The following examples are illustrative of catalysts which may be used in accordance with our invention:

Example 1 A base reforming catalyst having a composition of 76 mol percent alumina and 24 mol percent chromia, co-

of palladium chloride in a concentration of 0.09 mol per liter by permitting the catalyst to soak in such a solution in the proportions of 200 pounds of catalyst to 100 of t the aqueous solution of the palladium chloride at room temperature for one hour. The excess solution was drained from the 'catalyst, and it was dried at 300 F. for four hours. The catalyst was then heated for sixteen hours at 1000 F. in an atmosphere of dry nitrogen, cooled in nitrogen and bottled for testing. The catalyst contained 0.5 mol percent palladium oxide.

The same straight-run naphtha as described heretofore was passed through the resulting catalyst under the same conditions described heretofore. The Kattwinkel number of the reformed naphtha was 72 and the coke on the catalyst was 1.82%.- This'is an unusually high conversion level andthe extent of the coke formation is small as compared to the catalysts described heretofore, as can be seen by the following comparison:

Example 2 The above example was repeated except that the impregnating solution comprised platinum chloride and the amount of platinum oxide in the catalyst was 0.3 mol percent. Using the same naphtha and the same reforming conditions, the reformed product had a Kattwinkel number of 71 and the catalyst had a coke content of 2.55%. While in this example the amount of platinum oxide is half of the amountof palladium oxide in the previous example, the conversion level is nevertheless unusually high and the amount of coke well below amounts under commercial conditions, as is seen from the following comparison:

It is to be noted that the amount of platinumoxide or palladium oxide is quite small especially as compared with the amount of antimony described in the prior art component catalyst and that the results are attractive considering especially the relatively low hydrogen partial.

pressure and its advantages and the high conversion level and low coke formation indicated.

These results are attributed primarily to the addition of the third component oxide to a co-precipitated alumina-chromia base. It appears that the palladium or platinum oxide accomplishes its unusual promoter action because of the intimate association of the oxides comprising the base.

The third component is in the oxide form at the beginning of the reforming operation. It is believed to be in the oxide form after regeneration to burn off coke. During the reforming a part or all of the oxide may be reduced but because of the small amount it is diificult to ascertain the exact form of this component during the entire reforming operation.

It can readily be seen from the preceding discussion that the incorporation of very small amounts of the oxides of the platinum and palladium on an alumina-chromia co-precipitated base catalyst gives a substantial reduction in the rate of coke deposition at low hydrogen partial pressures as compared with the alumina-chromia base catalyst or other three component catalysts heretofore available.

The word chromia is used herein synonymously with chromium oxide.

We claim:

1. A process for catalytically reforming petroleum naphtha which comprises contacting said naphtha at a temperature in the range of about 800 to 1200 F. at a total pressure of about 0 to 100 p. s. i. g. at a hydrogen partial pressure of about 10 to 80 p. s. i. absolute with a co-precipitated alumina-chromia catalyst having 70 to 82 mol percent alumina, having 30 to 18 mol percent chromia, and containing as a third component an oxide selected from the group consisting of platinum oxide and palladium oxide in the proportions of about 0.001 to 1.0 mol percent based on the weight of the catalyst.

2. A process for catalytically reforming petroleum naphtha which comprises contacting said naphtha at a temperature of about 980 F. at a total pressure of about 25 p. s. i. g. at a hydrogen and at a partial pressure of about 33 p. s. i. absolute with a co-precipitated aluminachro-mia catalyst comprising about 75.8 mol percent alumina, about 23.9 mol percent chromia, and about 0.3 mol percent platinum oxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,236,514 Burk et a1. Apr. 1, 1941 2,317,683 Greensfelder Apr. 27, 1943 2,479,110 Haensel Aug. 16, 1949 2,635,082 Smith Apr. 14, 1953 2,678,923 Hansford May 18, 1954 

1. A PROCESS FOR CATALYTICALLY REFORMING PETROLEUM NAPHTHA WHICH COMPRISES CONTACTING SAID NAPHTHA AT A TEMPERATURE IN THE RANGE OF ABOUT 800 TO 1200*F. AT A TOTAL PRESSURE OF ABOUT 10 TO 80 P. S. O. ABSOLUTE WITH PARTIAL PRESSURE OF ABOUT 0 TO 100 P. S. I. G. AT A HYDROGEN A CO-OPRECIPITATED ALUMINA-CHROMIA CATALYST HAVING 70 TO 82 MOL PERCENT ALUMINA, HAVING 30 TO 18 MOL PERCENT CHROMIA, AND CONTAINING AS THIRD COMPONENT AN OXIDE SELECTED FROM THE GROUP CONSISTING OF PLATINUM OXIDE AND PALLADIUM OXIDE IN THE PROPORTIONS OF ABOUT 0.001 TO 1.0 MOL PERCENT BASED ON THE WEIGHT OF THE CATALYST. 